Considerable efforts have been made to provide an antistatic agent (commonly referred to as an "antistat") composition in a form which can be readily combined with various resins for extruding, molding or otherwise shaping plastic products which do not collect electrostatic charges on their surfaces. The present invention generally relates to an improved antistatic agent composition that is adapted to be formed into a free-flowing, non-dusting pellet which, in turn, may be added to known polymers to minimize, if not prevent, the marked tendency of polymers, such as thermoplastic polymers, to accumulate static charges. Such accumulation of static charges can result in the adherence of dust or other matter to the plastic products. Antistatic agents can be additives which migrate to the surface of a plastic, fiber or the like to modify its electrical properties.
Broadly, the antistatic agent pellet composition of the present invention includes an ethoxylated alkyl primary amine combined with a metal salt of a fatty acid such as a stearate or palmitate. The invention extends to a method of forming pellets from this composition. The composition can also advantageously include an antioxidant component which is included within the pelletized product. Ethoxylated amines have been used as antistatic agents in plastics. It has been common to make such amines from coconut or tallow-based products, resulting in liquid or paste forms of amines which are difficult to incorporate into conventional plastic material. A solid antistatic agent has been recognized as a preferred product, and U.S. Pat. No. 4,417,999, is directed to the forming of a solid antistatic agent using alkyl ethoxylated primary amines, the antistatic agent of this patent being in the form of a dried powder.
As reported in this patent, an alkyl ethoxylated primary amine that is predominantly 18 carbons in chain length, having a melting point of 50.degree.-52.degree. C., can be sprayed into a powder. However, once the powder is packaged or otherwise stored, it has been observed that it begins to lump and can continue to do so until its powdery condition is substantially lost. In an attempt to overcome this problem, it was found that if fumed silica or silica gel was mixed with the amine powder, lumping was prevented. This discovery constituted a substantial advance in the art because a non-lumping, free-flowing powder can be readily combined with polymeric materials to reduce, if not eliminate, the formation of electrostatic charges on the surfaces of articles formed from such polymeric materials.
The aforementioned antistatic powder does have its drawbacks. A powder produces dust on handling which can be undesirable because of potential health hazards as well as possible potential explosion hazards that can be attributed to dust producing materials. Also, somewhat closely controlled temperature conditions are required in storing and transporting powder products. A powder can be difficult to feed into or move through a material handling system, such as that utilizing screw augers. A powder can also be lost through small cracks or openings in material handling systems of the type that can be used in processing polymers into shaped forms such as sheets, films, filaments and molded plastic items.
By the present invention, an antistatic agent pellet composition is provided which combines an ethoxylated alkyl primary amine with a metal salt of a fatty acid such as a metal stearate, a metal palmitate or blends thereof. It has been found that the resulting composition may be readily pelletized thereby eliminating the disadvantages attendant to utilization of a powdered antistatic agent. The resulting pellets are free-flowing and non-dusting, thus eliminating any of the material storage, transporting and handling problems as well as the potential or perceived safety and health hazards mentioned above. The pellets may vary in size but are of sufficient size to prevent losses of antistatic agent through cracks or openings in a material handling system. The pellet composition is readily compatible with polymeric materials for addition thereto, such as by re-pelletizing therewith. In this manner, the antistatic agent is readily incorporated into an ultimately extruded, molded or otherwise formed plastic product that is substantially, if not completely, free of the propensity to collect electrostatic charges. In a preferred embodiment, a suitable antioxidant will be included in the composition, such an antioxidant being preferably in the form of a hindered phenol. The metal salt of fatty acid component is preferably zinc stearate or calcium stearate, although such stearate used in the composition in fact may be a blend of C.sub.18 stearate and C.sub.16 palmitate.
It is accordingly a general object of the present invention to provide an improved antistatic agent pellet composition and method of forming same.
Another object of the present invention is to provide an improved alkyl ethoxylated primary amine pellet composition including a metal stearate or the like and preferably, although not essentially, an antioxidant.
Another object of this invention is to provide a method for forming the alkyl ethoxylated primary amine pellets, wherein the feed rate of the ingredients of the pellet composition into the pelletizing mill is on the order of approximately 1000 to 1200 pounds per hour.
Another object of the invention is to provide an essentiall C.sub.18 alkyl ethoxylated primary amine antistatic agent pellet which is free-flowing, non-dusting, non-sticky, and is not susceptible to lumping, and which is adapted for addition to polymeric material for the extrusion, molding or other formation of plastic articles.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.